Field Of The Invention
This invention relates to heating, cooling and air conditioning systems, and more broadly to systems supplying a source of hot, dry gas available upon demand and irrespective of availability of conventional energy heat sources.
Nominally free energy sources such as the sun, waste heat from commercial buildings and industrial operations by way of heat reclaim can augment and supplement conventional heating and cooling systems or systems designed to provide hot, dry gas, such as air, to dry hay, seeds, clothes, lumber, various paint finishes, etc. at a steady rate or when needed, particularly where the original source of heat is not available when and at the time the energy is needed.
Conventionally, solar systems have employed water, rocks, earth, etc., as means to store heat for future use, but such storage systems are highly inefficient and are rather massive in size.
Desiccants constitute materials which attract moisture to their surfaces. Practical desiccants constitute generally granular material having many openings and pores such that the surface area exposed to the gas or air inside the grain is many times the area of the grain exterior or what appears to be the surface of the grain. Given some time, water molecules can occupy all of the outside and inside surfaces allowing the material to hold large quantities of water and surface bondage without showing wetness and before loosing its attraction for additional moisture.
For instance, a pound of silica gel can absorb 50% of its dry weight in water without becoming damp to the feel and before loosing all of its attraction for moisture. Activated aluminate can hold 30% of its dry weight in water in a similar manner. These figures are directed only to the moisture which may be held to the surfaces of these elements by an attraction known as surface absorption. This attraction is greatest when the material is dried of all attached moisture, and such desiccants readily attract water from the humidity of the gas, such as air, until the gas is at least as dry as the desiccant. This application is directed to the employment of a readily available gas, such as air, as the circulation media, and it is intended that reference to air within this application infers that the air may be readily substituted by other gases. Likewise, dry gases will evaporate water from that held by the surface of the desiccants until the desiccant is as dry as the gas. Large beds of desiccants are often used for exact humidity control because these characteristics can stabilize the moisture in air passing over them.
The measure of dryness that most closely parallels in desiccants and in gases is the psychometric depression, with a number of degrees that the wet bulb of a thermometer drops below the dry bulb of another when the wet bulb is wetted with distilled water and a gas is circulated over both bulbs. From this, the dryness of both air and desiccant may be stated in comparable terms. When a desiccant and a gas are in equilibrium, they are said to have the same depression.
Water vapor, when attracted to the surface of a desiccant, takes on liquid form or state, and the heat of vaporization is released, plus a 20% wetting factor, amounting to about 1,200 BTU's per pound of water condensed. Thus, one pound of a very dry silica gel (having a depression of 60.degree. F.) will release 600 BTU's from saturated air where all of the attraction for water is used. Likewise, the same amount of heat is absorbed by the water vapor when spent desiccant (wet) is dried by air having a depression of 60.degree. or better, causing the air and the desiccant to be cooled according to the heat so removed. The sensible heat goes into the vaporization of water, and in separating the water from the desiccant, the reverse of the wetting process.
This principle works as well when the material is only partially cycled, either taking on or giving up moisture--that is, is neither completely dry nor completely wet. The amount of heat released or absorbed by these processes is reduced by the portion that the full cycle is not used. The full cycle value for activated aluminate is approximately 360 BTU's.
The present invention, therefore, is directed to the utilization of desiccants to store energy from inadequate, periodic or undependable sources of heat for delivery in the amount needed and as the need arises, permitting a storage system due to the characteristics of the desiccants which is of reduced size, weight with a high percentage of recovery, even after long storage.
It is an object of the present invention to provide a heating and/or cooling system of this type in which energy may be supplied to the system and the desiccant dried by solar heat, the waste heat from a refrigeration condensor, waste heat from a stove functioning in cooking and heating processes, waste heat from industrial processes and by drying gases from whatever source, even if the gases are not hot. Desiccant material so dried may be stored almost indefinitely in its dry state with little loss of potential energy return, and the energy may be used at any time desired to produce drying air, heat or cooling for room conditioning of living space, as well as for various other purposes.